The perplexing picture painted by our background investigation of the metals lab facility described in our last issue came even more into focus during our walk-thru inspection.

The “metal-free” lab had HEPA filters with aluminum separators.

There was obviously a negative pressure in the cleanroom but in the absence of local instrumentation, was not measurable. We did note a number of cabinet doors were standing wide open. Attempts to close them resulted in their flying open again due to high pressure differential between cabinet interiors that were tied in to wall cavities open to an uncontrolled ceiling space, and the cleanroom.

The horizontal flow room HEPA filters had a pressure drop that “pegged” the filter differential pressure gage. We were told that several filters had flown off the wall and across the room at one point as a result of this high pressure.

Since there was no specification of cleanliness there was no “pass-fail” particle count criterion. A quick “white glove” test demonstrated that the bench tops and other horizontal surfaces of the cleanroom were dust laden, probably due to negative cleanroom pressure drawing in dirt from surrounding spaces.

Air noise was very high.

Our recommendations included: meeting with the EH&S people to convince them that the exhaust hoods in the lab can control the toxic fumes as is done routinely in similar positive pressure cleanrooms; provide local maintenance oversight by user personnel to monitor prefilter and HEPA filter loading, room pressurization, temperature/humidity etc.; obtain baseline particle count data and institute a periodic monitoring/certification program. Incidentally the user finally admitted that a Class 1000 (ISO 6) cleanroom would be nice.

Why did this happen?

In 1983, the advisory contained in the previous column was warranted. It would appear that in 2003 it is still good advice. There is a perceived level of expertise that may, in fact, be illusory. Many engineering and facilities folks have heard the term “cleanroom.” Cleanrooms are no longer new. They are integral to a wide variety of high-tech facilities. Yet many competent design practitioners become defensive when it is suggested they may not be expert in this arena.

There is a set of rules that is unique to cleanroom design, and when the rules are followed the result is not in doubt. There is much more guidance available today than 20 years ago. Yet we continue to see problems that arise as a result of poor communication, poor conceptual design, incorrect application of “rules of thumb,” lack of proper project oversight and coordination, poor maintenance knowledge, and inappropriate attention to detail regarding monitoring and operating the clean facility.

Indeed, the more things change, the more they remain the same.